Flexible display

ABSTRACT

Disclosed is a flexible display. The flexible display includes: a base layer which including a first portion having a first surface on which an organic light emitting element is disposed and a second portion extending from the outside of the first portion and bent toward a second surface opposing to the first surface; a protective film covering at least a part of the second portion to suppress permeation of moisture; a polarization layer disposed on the organic light emitting element of the first portion without having a barrier film between the polarization layer and the base layer; and a resin filled between the polarization layer and the protective film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.10-2016-0110581 filed on Aug. 30, 2016, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND Field

The present disclosure relates to a flexible display.

Description of the Related Art

An image display device which implements various information on a screenis core technology of the information and telecommunication age and isbeing developed to be thinner, lighter, and more portable, and havehigher performance. One example of an image display device are organiclight emitting display devices that are configured to display an imageby controlling the amount of light emitted from an organic lightemitting element.

The organic light emitting element is a self-emitting element that usesa thin light emitting layer between electrodes. A typical organic lightemitting display device has a structure in which a pixel driving circuitand the organic light emitting element are formed on a substrate, andlight emitted from the organic light emitting element passes through thesubstrate or a barrier layer to display an image.

The organic light emitting display device is implemented without aseparate light source, and thus, it can be implemented as a flexibledisplay. In this case, a flexible material such as plastic or metal foilmay be used as a substrate of the organic light emitting display device.

SUMMARY

According to an aspect of the present disclosure, there is provided aflexible display. The flexible display includes a base layer including afirst portion having a first surface on which an organic light emittingelement is disposed and a second portion extending from the outside ofthe first portion and bent toward a second surface opposite to the firstsurface, a protective film covering at least a part of the secondportion to suppress permeation of moisture, a polarization layerdisposed on the organic light emitting element of the first portionwithout a barrier film between the polarization layer and the protectivefilm, and a resin filled between the polarization layer and theprotective film.

According to another embodiment of the present disclosure, there isprovided a flexible display. The flexible display includes a base layer,an organic light emitting element, a polarization layer, a protectivefilm, and a resin. The base layer includes a flat portion and a curvedportion connected to the flat portion. The organic light emittingelement is disposed on the flat portion of the base layer. Thepolarization layer is disposed on the organic light emitting portion.The protective film is disposed on the curved portion of the base layer.The resin is filled between the polarization layer and the protectivefilm. The resin is in contact with at least a side surface of thepolarization layer and a first side surface of the protective film.

Other detailed matters of the embodiments are included in the detaileddescription and the drawings.

According to the embodiments of the present disclosure, a structure anda component which reduce a damage applied to a bend portion of theflexible display may be provided. More specifically, according to theembodiments of the present disclosure, a coating layer which mayuniformly protect a bend allowance section may be provided. Therefore,in the flexible display according to the embodiment of the presentdisclosure, a failure caused in the bend portion may be reduced and areliability of a product may be improved. The effects according to thepresent disclosure are not limited to the contents exemplified above,and more various effects are included in the present specification.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a flexible display which may be incorporated inelectronic devices, according to an embodiment of the presentdisclosure;

FIG. 2 illustrates an arrangement of a flat portion and a bend portion,according to an embodiment of the present disclosure;

FIGS. 3A and 3B illustrate an arrangement of a active area of a flexibledisplay, according to an embodiment of the present disclosure;

FIG. 4 a cross-sectional view illustrating a simplified stack structureof a flexible display according to embodiment of the present disclosure;

FIG. 5 illustrates a plane view and a cross-sectional view of bendingpatterns according to an embodiment of the present disclosure;

FIGS. 6A to 6C are simplified cross-sectional views illustrating anarrangement of elements in the flexible display;

FIGS. 7A and 7B each illustrates a structure of a multi-layeredconductive line, according to an embodiment of the present disclosure;

FIG. 8 illustrates a strain-reducing trace designs, according to anembodiment of the present disclosure;

FIGS. 9A and 9B illustrate a simplified view of a wire trace having aplurality of sub traces, according to an embodiment of the presentdisclosure;

FIG. 10 illustrates an arrangement of multiple wire traces having adiamond trace design, according to an embodiment of the presentdisclosure;

FIGS. 11A and 11B illustrate simplified cross-sectional views of a wiretrace, according to an embodiment of the present disclosure;

FIGS. 12A and 12B illustrate simplified views of a strain-reducing wiretrace having a modified part, according to an embodiment of the presentdisclosure;

FIGS. 13A to 13C are views illustrating a configuration of a protectivecoating layer used for a flexible display, according to an embodiment ofthe present disclosure;

FIGS. 14A and 14B are views illustrating a flexible display to which aprotective coating layer is applied, according to an embodiment of thepresent disclosure;

FIGS. 15A and 15B are views illustrating a protective coating layer usedfor a flexible display, according to another embodiment of the presentdisclosure; and

FIGS. 16A to 16D are views illustrating a protective film used for aflexible display, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Advantages and characteristics of the present disclosure, and a methodof achieving the advantages and characteristics will be clear byreferring to the embodiments described below in detail together with theaccompanying drawings. However, the present disclosure is not limited tothe embodiment disclosed herein but will be implemented in variousforms. The embodiments are provided by way of example only so that aperson of ordinary skilled in the art can fully understand thedisclosures of the present disclosure and the scope of the presentdisclosure. Therefore, the present disclosure will be defined only bythe scope of the appended claims.

The shapes, sizes, ratios, angles, numbers, and the like illustrated inthe accompanying drawings for describing the various embodiments of thepresent disclosure are merely examples, and the present disclosure isnot limited thereto. Like reference numerals generally denote likeelements throughout the specification. Further, in the followingdescription of the present disclosure, a detailed explanation of knownrelated technologies may be omitted to avoid unnecessarily obscuring thesubject matter of the present disclosure. The terms such as “including,”“having,” and “consist of” used herein are generally intended to allowother components to be added unless the terms are used with the term“only”. Any references to singular may include plural unless expresslystated otherwise. Components are interpreted to include an ordinaryerror range even if not expressly stated.

When the position relation between two parts is described using theterms such as “on”, “above”, “below”, and “next”, one or more parts maybe positioned between the two parts unless the terms are used with theterm “immediately” or “directly”. When an element or layer is disposed“on” other element or layer, another layer or another element may beinterposed directly on the other element or therebetween. If it isdescribed that a component is “connected” or “coupled” to anothercomponent, it is understood that the component is directly connected orcoupled to the other component but another component may be “connected”or “coupled” between the components.

Although the terms “first”, “second”, and the like are used fordescribing various components, these components are not confined bythese terms. These terms are merely used for distinguishing onecomponent from the other components. Therefore, a first component to bementioned below may be a second component in a technical concept of thepresent disclosure.

A size and a thickness of each component illustrated in the drawing areillustrated for convenience of description, and the present disclosureis not limited to the size and the thickness of the componentillustrated. Hereinafter, various embodiments of the present disclosurewill be described in detail with reference to accompanying drawings.

FIG. 1 illustrates a flexible display which may be incorporated inelectronic devices, according to an embodiment of the presentdisclosure.

The flexible display refers to a display device provided withflexibility and may be used as the same meanings as a bendable displaydevice, a rollable display device, a unbreakable display device, or afoldable display device. Referring to FIG. 1, the flexible display 100includes at least one display area (i.e., active area), in which anarray of pixels are formed therein. One or more non-display (i.e.,inactive area) may be provided at the periphery of the active area. Thatis, the inactive area may be adjacent to one or more sides of the activearea. In FIG. 1, the inactive area surrounds a rectangular shape activearea. However, it should be appreciated that the shapes of the activearea and the shapes/the arrangement of the inactive area adjacent to theactive area are not particularly limited to flexible display 100illustrated in FIG. 1. The active area and the inactive area may be inany shape suitable to the design of the electronic device employing theflexible display 100. Non-limiting examples of the active area shapes inthe flexible display 100 include a pentagonal shape, a hexagonal shape,a circular shape, an oval shape, and more.

Each pixel in the active area may be associated with a pixel circuit,which includes at least one switching thin-film transistor (TFT) and atleast one driving TFT on the backplane of the flexible display 100. Eachpixel circuit may be electrically connected to a gate line and a dataline to communicate with one or more driving circuits, such as a gatedriver and a data driver positioned in the inactive area of the flexibledisplay 100.

For example, one or more driving circuits may be implemented with TFTsfabricated in the inactive area as depicted in FIG. 1. The drivingcircuit may be referred to as a gate-in-panel (GIP). Also, some of thecomponents, such as data drive-IC, may be mounted on a separate printedcircuit board and coupled to a connection interface (Pads/Bumps, Pin,etc.) disposed in the inactive area using a printed circuit film such asflexible printed circuit board (FPCB), chip-on-film (COF),tape-carrier-package (TCP) or any other suitable technologies. Theinactive area with the connection interface can be bent away so that theprinted circuit film (e.g., COF, FPCB and the like) is positioned at therear side of the flexible display 100.

The flexible display 100 may include various additional components forgenerating a variety of signals or otherwise driving the pixels in theactive area. Non limiting examples of the components for driving thepixels include an inverter circuit, a multiplexer, an electrostaticdischarge (ESD) circuit and the like. The flexible display 100 may alsoinclude components associated with functionalities other than fordriving the pixels of the flexible display 100. For instance, theflexible display 100 may include components for providing a touchsensing functionality, a user authentication functionality (e.g., fingerprint scan), a multi-level pressure sensing functionality, a tactilefeedback functionality and/or various other functionalities for theelectronic device employing the flexible display 100. Some of theaforementioned components can be placed in the inactive area of theflexible display 100 and/or on a separate printed circuit that isconnected to the connection interface of the flexible display 100.

Multiple parts of the flexible display 100 can be bent along the bendingline BL. The bending line BL in the flexible display 100 may extendhorizontally (e.g., X-axis shown in FIG. 1), vertically (e.g., Y-axisshown in FIG. 1) or even diagonally. Accordingly, the flexible display100 can be bent in any combination of horizontal, vertical and/ordiagonal directions based on the desired design of the flexible display100.

One or more edges of the flexible display 100 can be bent away from theplane of the central portion 101 along the bending line BL. Although thebending line BL is depicted as being located near the edges of theflexible display 100, it should be noted that the bending lines BL canextend across the central portion 101 or extend diagonally at one ormore corners of the flexible display 100. Such configurations wouldallow the flexible display 100 to provide a foldable display or adouble-sided display having display pixels on both outer sides of afolded display.

With the ability to bend one or more portions of the flexible display100, part of the flexible display 100 may be defined as a substantiallyflat portion and a bend portion. A part of the flexible display 100 mayremain substantially flat and referred to as a central portion 101 ofthe flexible display 100. A part of the flexible display 100 may be bentin a certain bend angle from the plane of an adjacent portion, and suchportion is referred to as a bend portion 102 of the flexible display100. The bend portion 102 includes a bend allowance section, which canbe actively curved in a certain bend radius.

It should be understood that the term “substantially flat” includes aportion that may not be perfectly flat. For example, the concave centralportion 101 a and the convex central portion 101 b depicted in FIG. 2may be described as a substantially flat portion in some embodimentsdiscussed in the present disclosure. In FIG. 2, one or more bendportions 102 exist next to the convex central portion 101 a or concavecentral portion 101 b, and bent inwardly or outwardly along the bendingline BL in a bend angle about a bend axis. The bend radius of the bendportion 102 is smaller than the bend radius of the central portion (101a, 101 b). In other words, the term “substantially flat portion” refersto a portion with a lesser curvature than that of an adjacent bendallowance section of the flexible display 100.

Depending on the location of the bending line BL in the flexible display100, a portion on one side of the bending line BL may be positionedtoward the center of the flexible display 100, whereas the portion onthe opposite side of the bending line BL is positioned toward an edgeportion of the flexible display 100. The portion toward the center maybe referred to as the central portion and the portion toward the edgemay be referred to as the edge portion of the flexible display 100.Although this may not always be the case, a central portion of theflexible display 100 can be the substantially flat portion and the edgeportion can be the bend portion of the flexible display 100. It shouldbe noted that a substantially flat portion can also be provided in theedge portion of the flexible display 100. Further, in some configurationof the flexible display 100, a bend allowance section may be positionedbetween two substantially flat portions.

Bending the inactive area reduces the extent of which the inactive areais visible from the front side of the assembled flexible display 100.Part of the inactive area that remains visible from the front side canbe covered with a bezel. The bezel may be formed, for example, from astand-alone bezel structure that is mounted to the cover layer 114, ahousing or other suitable components of the flexible display 100. Theinactive area remaining visible from the front side may also be hiddenunder an opaque masking layer, such as black ink (e.g., a polymer filledwith carbon black). Such an opaque masking layer may be provided on aportion of various layers included in the flexible display 100, such asa touch sensor layer, a polarization layer, a cover layer, and othersuitable layers.

In some embodiments, the bend portion of the flexible display 100 mayinclude an active area capable of displaying image from the bendportion, which is referred herein after as the second active area. Thatis, the bending line BL can be positioned in the active area so that atleast some display pixels of the active area is included in the bendportion of the flexible display 100.

FIGS. 3A and 3B each illustrates an arrangement of active areas in anembodiment of flexible display 100 of the present disclosure. In thearrangement depicted in FIG. 3A, the matrix of pixels in the secondactive area of the bend portion may be continuously extended from thematrix of the pixels in the active area of the central portion 101.Alternatively, in the arrangement depicted in FIG. 3B, the second activearea within the bend portion 102 and the active area within the centralportion 101 of the flexible display 100 may be separated apart from eachother by the bend allowance section of the flexible display 100. Somecomponents in the central portion 101 and the bend portion 102 can beelectrically connected via one or more conductive line 120 laid acrossthe bend allowance section of the flexible display 100.

The pixels in the second active area and the pixels in the centralactive area may be addressed by the driving circuits (e.g., gate driver,data driver, etc.) as if they are in a same matrix. In this case, thepixels of the central active area and the pixels of the second activearea may be operated by the same set of driving circuits. By way ofexample, the Nth row pixels of the central active area and the Nth rowpixels of the second active area may be configured to receive the gatesignal from the same gate driver. As shown in FIG. 3B, the part of thegate line crossing over the bend allowance section or a bridge forconnecting the gate lines of the two active areas may have astrain-reducing design.

Depending on the functionality of the second active area, the pixels ofthe second active area can be driven discretely from the pixels in thecentral active area. That is, the pixels of the second active area maybe recognized by the display driving circuits as being an independentmatrix of pixels separate from the matrix of pixels of the centralactive area. In such cases, the pixels of the second active area mayreceive signals from at least one discrete driving circuit other than adriving circuit for providing signals to the pixels of the centralactive area.

Regardless of the shape, the second active area in the bend portion mayserve as a secondary active area in the flexible display 100. Also, thesize of the second active area is not particularly limited. The size ofthe second active area may depend on its functionality within theelectronic device. For instance, the second active area may be used toprovide images and/or texts such a graphical user interface, buttons,text messages, and the like. In some cases, the second active area maybe used to provide light of various colors for various purposes (e.g.,status indication light), and thus, the size of the second active areaneed not be as large as the active area in the central portion of theflexible display 100.

FIG. 4 illustrates a simplified stack structure of components in anflexible display according to an embodiment of the present disclosure.For convenience of explanation, the central portion 101 of the flexibledisplay 100 is illustrated as being substantially flat, and the bendportions 102 are provided at the edges of the flexible display 100 inFIG. 4.

As shown, one or more bend portions 102 may be bent away from thecentral portion 101 in a certain bend angle θ and with a bend radius Rabout the bending axis. The size of each bend portion 102 that is bentaway from the central portion needs not be the same. That is, the lengthfrom the bending line BL to the outer edge of the base layer 106 at eachbend portion 102 can be different from other bend portions. Also, thebend angle θ around the bend axis and the bend radius R from the bendaxis can vary between the bend portions 102.

In the example shown in FIG. 4, the right side bend portion 102 has thebend angle θ of 90°, and the bend portion 102 includes a substantiallyflat section. A bend portion 102 can be bent at a larger bend angle θ,such that at least some part of the bend portion comes underneath theplane of the central portion 101 of the flexible display 100 as the bendportion 102 on the left side of the flexible display 100. Also, a bendportion 102 can be bent at a bend angle θ that is less or 90°.

In some embodiments, the radius of curvatures (i.e., bend radius) forthe bend portions 102 in the flexible display 100 may be between about0.1 mm to about 10 mm, more preferably between about 0.1 mm to about 5mm, more preferably between about 0.1 mm to about 1 mm, more preferablybetween about 0.1 mm to about 0.5 mm. In some embodiments, the bendradius at a bend portion 102 of the flexible display 100 may be lessthan 0.5 mm.

One or more support layers 108 may be provided at the underside of thebase layer 106 to increase rigidity and/or ruggedness at the selectiveportion of the flexible display 100. For instance, the support layer 108can be provided on the underside surface of the base layer 106 at thecentral portions 101 of the flexible display 100. The support layer 108may not be provided in the bend allowance section to allow for increasedflexibility. The support layer 108 may be provided on the bend portion101 that is positioned under the central portion 101 of the flexibledisplay 100. Increased rigidity at selective parts of the flexibledisplay 100 may help in increasing the accuracy of the configuration andplacement of various components during manufacturing and using theflexible display 100. The support layer 108 can also serve to reduce thelikelihood generation of cracks in the base layer 106, if the base layer106 has a higher modulus than the support layer 108.

The base layer 106 and the support layer 108 may each be made of a thinplastic film formed from polyimide, polyethylene naphthalate (PEN),polyethylene terephthalate (PET), a combination of other suitablepolymers, etc. Other suitable materials that may be used to form thebase layer 106 and the support layer 108 include, a thin glass, a metalfoil shielded with a dielectric material, a multi-layered polymer stackand a polymer composite film comprising a polymer material combined withnanoparticles or micro-particles dispersed therein, etc. Support layers108 provided in various parts of the flexible display 100 need not bemade of the same material. For example, a thin-glass layer may be usedas a support layer 108 for the central portion 101 of the flexibledisplay 100 while a plastic film is used as a support layer 108 for edgeportions.

The thickness of the base layer 106 and the support layer 108 is anotherfactor to consider in designing the flexible display 100. On the onehand, bending of the base layer 106 at a small bend radius can bedifficult if the base layer 106 has excessively high thickness. Also,excessive thickness of the base layer 106 can increase mechanical stressto the components disposed thereon during bending the base layer 106. Onthe other hand, however, the base layer 106 can be too fragile to serveas a substrate for supporting various components of the flexible displayif it is too thin.

To ease the bending of the substrate while providing sufficient support,the base layer 106 may have a thickness in a range of about from 5 μm toabout 50 μm, more preferably in a range of about 5 μm to about 30 μm,and more preferably in a range of about 5 μm to about 16 μm. The supportlayer 108 may have a thickness from about 100 μm to about 125 μm, fromabout 50 μm to about 150 μm, from about 75 μm to 200 μm, less than 150μm, or more than 100 μm.

In one embodiment, a layer of polyimide with a thickness of about 10 μmto about 16 μm serves as the base layer 106 while a polyethyleneterephthalate (PET) layer with a thickness of about 50 μm to about 125μm serves as the support layer 108. In another embodiment, a layer ofpolyimide with a thickness of about 10 μm to about 16 μm serves as thebase layer 106 while a thin-glass layer with a thickness of about 50 μmto about 200 μm is used as the support layer 108. In yet anothersuitable configuration, a thin glass layer is used as the base layer 106with a layer of polyimide serving as the support layer 108 to reduce thelikelihood of breaking of the base layer 106.

During manufacturing, some parts of the flexible display 100 may beexposed to external light. Some materials used in fabricating thecomponents on the base layer 106 or the components themselves mayundergo undesirable state changes (e.g., transition of threshold voltagein the TFTs) due to the light exposure during the manufacturing of theflexible display 100. Some parts of the flexible display 100 may be moreheavily exposed to the external light than others, and this can lead toa display non-uniformity (e.g., mura, shadow defects, etc.). To reducethe impact of such problems, the base layer 106 and/or the support layer108 may include one or more materials capable of reducing the amount ofexternal light.

The light blocking material, for instance chloride modified carbonblack, may be mixed in the constituent material of the base layer 106(e.g., polyimide or other polymers). In this way, the base layer 106 maybe formed of polyimide with a shade to provide a light blockingfunctionality. Such a shaded base layer 106 can also improve thevisibility of the image content displayed on the flexible display 100 byreducing the reflection of the external light coming in from the frontside of the flexible display 100.

Instead of the base layer 106, the support layer 108 may include a lightblocking material to reduce the amount of light coming in from the rearside (i.e., the support layer 108 attached side) of the flexible display100. The constituent material of the support layer 108 may be mixed withone or more light blocking materials in a similar fashion as describedabove. Furthermore, both the base layer 106 and the support layer 108can include one or more light blocking materials. Here, the lightblocking materials used in the base layer 106 and the support layer 108need not be the same.

While making the base layer 106 and the support layer 108 to block theunwanted external light may improve display uniformity and reducereflection as described above, recognizing alignment marks for accuratepositioning of the components or for carrying out manufacturing processmay become difficult. For example, accurate positioning of thecomponents on the base layer 106 or the alignment during bending of theflexible display 100 can be difficult as the positioning of the layersmay need to be determined by comparing the outer edges of theoverlapping portions of the layer(s). Further, checking for unwanteddebris or other foreign materials in the flexible display 100 can beproblematic if the base layer 106 and/or the support layer 108 blocks anexcessive range(s) of light spectrum (i.e., wavelengths in the visible,the ultraviolet, and the infrared spectrum).

Accordingly, in some embodiments, the light blocking material, which maybe included in the base layer 106 and/or the support layer 108 isconfigured to pass the light of certain polarization and/or the lightwithin specific wavelength ranges usable in one or more manufacturingand/or testing processes of the flexible display 100. By way of example,the support layer 108 may pass the light to be used in quality checkand/or alignment processes (e.g., UV, IR spectrum light) during themanufacturing the flexible display 100, but block the light in thevisible light wavelength range. The limited range of wavelengths canhelp reduce the display non-uniformity problem, which may be caused bythe shadows generated by the printed circuit film attached to base layer106, especially if the base layer 106 includes the light blockingmaterial as described above.

The base layer 106 and the support layer 108 can work together inblocking and passing specific types of light. For instance, the supportlayer 108 can change the polarization of light, such that the light willnot be passable through the base layer 106. This way, certain type oflight can be passed through the support layer 108 for various purposesduring manufacturing of the flexible display 100, but unable to passthrough the base layer 106 to cause undesired effects to the componentsdisposed on the opposite side of the base layer 106.

Backplane of the flexible display 100 is implemented on the base layer106. In some embodiments, the backplane of the flexible display 100 canbe implemented with TFTs using low-temperature poly-silicon (LTPS)semiconductor layer as its active layer. In one example, the pixelcircuit and the driving circuits (e.g., GIP) on the base layer 106 areimplemented with NMOS LTPS TFTs. In other example, the backplane of theflexible display 100 can be implemented with a combination of NMOS LTPSTFTs and PMOS LTPS TFTs. For instance, the driving circuit (e.g., GIP)on the base layer 106 may include one or more CMOS circuits to reducethe number of lines for controlling the scan signals on the gate line.

Furthermore, in some embodiments, the flexible display 100 may employmultiple kinds of TFTs to implement the driving circuits in the inactivearea and/or the pixel circuits in the active area. That is, acombination of an oxide semiconductor TFT and an LTPS TFT may be used toimplement the backplane of the flexible display 100. In the backplane,the type of TFTs may be selected depending to the operating conditionsand/or requirements of the TFTs within the corresponding circuit.

Low-temperature-poly-silicon (LTPS) TFTs generally exhibit excellentcarrier mobility even at a small profile, making them suitable forimplementing integrated driving circuits. The carrier mobility of theLTPS TFT makes it suitable for components having a fast speed operation.Despite the aforementioned advantages, initial threshold voltages mayvary among the LTPS TFTs due to the grain boundary of thepoly-crystalized silicon semiconductor layer.

A TFT employing an oxide material based semiconductor layer, such as anindium-gallium-zinc-oxide (IGZO) semiconductor layer (referredhereinafter as “the oxide TFT”), is different from the LTPS TFT in manyrespects. Despite a lower mobility than the LTPS TFT, the oxide TFT isgenerally more advantageous than the LTPS TFT in terms of powerefficiency. Low leakage current of the oxide TFT during its off stateallows to remain in active state longer. This can be advantageous fordriving the pixels at a reduced frame rate when a high frame rate fordriving the pixels is not needed.

By way of example, the flexible display 100 may be provided with afeature in which the pixels of the entire active area or selectiveportion of the active area are driven at a reduced frame rate under aspecific condition. In this setting, the pixels can be refreshed at areduced refresh rate depending on the content displayed from theflexible display 100. Also, part of the active area displaying a stillimage data (e.g., user interface, text) may be refreshed at a lower ratethan other part of the active area displaying rapidly changing imagedata (e.g., movie). The pixels driven at a reduced refresh rate may havean increased blank period, in which the data signal is not provided tothe pixels. This would minimize the power wasted from providing thepixels with the same image data. In such embodiments, some of the TFTsimplementing the pixel circuits and/or the driving circuits of theflexible display 100 can be formed of the oxide TFT to minimize theleakage current during the blank period. By reducing the current leakagefrom the pixel circuits and/or the driving circuits, the pixels canachieve more stable level of luminance even when the display isrefreshed at a reduced rate.

Another feature of the oxide TFT is that it does not suffer from thetransistor-to-transistor initial threshold voltage variation issue asmuch as the LTPS TFTs. Such a property can be advantageous whenincreasing the size of the flexible display 100. Threshold shifts underbias stress is also different between LTPS TFT and oxide TFT.

Considering the aforementioned characteristics of LTPS TFT and oxideTFT, some embodiments of the flexible display 100 disclosed herein canemploy a combination of the LTPS TFT and the oxide TFT in a singlebackplane. In particular, some embodiments of the flexible display 100can employ LTPS TFTs to implement the driving circuits (e.g., GIP) inthe inactive area and employ oxide TFTs to implement the pixel circuitsin the active area. Due to the carrier mobility of the LTPS TFTs,driving circuits implemented with LTPS TFTs may operate at a fasterspeed than the driving circuits implemented with the oxide TFTs. Inaddition, more integrated driving circuits can be provided with the LTPSTFT, which reduces the size of the inactive area in the flexible display100. With the improved voltage holding ratio of the oxide TFTs used inthe pixel circuits, leakage current from the pixels can be reduced. Thisalso enables to drive pixels in a selective portion of the active areaor to drive pixels at a reduced frame rate under a predeterminedcondition (e.g., when displaying still images) while minimizing displaydefects caused by the leakage current.

In some embodiments, the driving circuits in the inactive area of theflexible display 100 may be implemented with a combination of N-TypeLTPS TFTs and P-Type LTPS TFTs while the pixel circuits are implementedwith oxide TFTs. For instance, N-Type LTPS TFTs and P-Type LTPS TFTs canbe used to implement a CMOS gate driver (e.g., CMOS GIP, Data Driver)whereas oxide TFTs are employed in at least some part of the pixelcircuits. Unlike the GIP formed entirely of either the P-type or N-typeLTPS TFTs, the gate out signal from the CMOS gate driver can becontrolled by DC signals or logic high/low signals. This allows for morestable control of the gate line during the blank period such that thesuppression of current leakage from the pixel circuit or unintendedactivation of the pixels connected the gate line can be achieved.

A CMOS gate driver or an inverter circuit on the backplane can beimplemented by using a combination of LTPS TFTs and oxide TFTs. Forinstance, a P-type LTPS TFT and an N-Type oxide TFT can be used toimplement a CMOS circuit. Also, the pixel circuits in the active areacan also be implemented by using both the LTPS TFTs and the oxide TFTs.When employing both kinds of TFTs in the pixel circuit and/or thedriving circuit, the LTPS TFT can be strategically placed within thecircuit to remove bias remaining in a node between oxide TFTs duringtheir off state and minimize the bias stress (e.g., PBTS, NBTS). Inaddition, the TFTs in a circuit, which are connected to a storagecapacitor, can be formed of the oxide TFT to reduce leakage currenttherefrom.

The organic light-emitting diode (OLED) element layer 150 is disposed onthe base layer 106. The OLED element layer 150 includes a plurality ofOLED elements, which is controlled by the pixel circuits and the drivingcircuits implemented on the base layer 106 as well as any other drivingcircuits connected to the connection interfaces on the base layer 106.The OLED element layer includes an organic-light emitting materiallayer, which may emit light of certain spectral color (e.g., red, green,blue). In some embodiments, the organic-light emitting material layermay have a stack configuration to emit white light, which is essentiallya combination of multiple colored lights.

The encapsulation 104 is provided to protect the OLED element layer 150from air and moisture. The encapsulation 104 may include multiplematerials of layers for reducing permeation of air and moisture toprotect OLED elements thereunder. In some embodiments, the encapsulation104 may be provided in a form of a thin film.

The flexible display 100 may include a polarization layer 110 forcontrolling the display characteristics (e.g., external lightreflection, color accuracy, luminance, etc.) of the flexible display100. Also, the cover layer 114 may be used to protect the flexibledisplay 100.

Electrodes for sensing touch input from a user may be formed on aninterior surface of a cover layer 114 and/or at least one surface of thepolarization layer 110. If desired, an independent layer with the touchsensor electrodes and/or other components associated with sensing oftouch input (referred hereinafter as touch-sensor layer 112) may beprovided in the flexible display 100. The touch sensor electrodes (e.g.,touch driving/sensing electrodes) may be formed from transparentconductive material such as indium tin oxide, carbon based materialslike graphene or carbon nanotube, a conductive polymer, a hybridmaterial made of mixture of various conductive and non-conductivematerials. Also, metal mesh such as aluminum mesh, silver mesh, etc. canalso be used as the touch sensor electrodes.

The touch sensor layer 112 may include one or more deformable dielectricmaterials. One or more electrodes may be interfaced with or positionednear the touch sensor layer 112, and read signals measuring electricalchanges upon deformation of the electrodes. The measurement may beanalyzed to assess several levels of the amount of pressure on theflexible display 100.

In some embodiments, the touch sensor electrodes can be utilized inidentifying the location of the user inputs as well as assessing thepressure of the user input. Identifying the location of touch input andmeasuring of the pressure of the touch input on the flexible display 100may be achieved by measuring changes in capacitance from the touchsensor electrodes on one side of the touch sensor layer 112. The touchsensor electrodes and/or other electrode may be used to measure a signalindicative of the pressure on the flexible display 100 by the touchinput. Such a signal may be obtained simultaneously with the touchsignal from the touch sensor electrodes or obtained at a differenttiming.

The deformable material included in the touch sensor layer 112 may be anelectro-active material, which the amplitude and/or the frequency of thedeformable material is controlled by an electrical signal and/orelectrical field. The examples of such deformable materials includepiezo ceramic, electro-active-polymer (EAP) and the like. Accordingly,the touch sensor electrodes and/or separately provided electrode canactivate the deformable material to bend the flexible display 100 todesired directions. In addition, such electro-active materials can beactivated to vibrate at desired frequencies, thereby providing tactileand/or texture feedback on the flexible display 100. The flexibledisplay 100 may employ a plurality of electro-active material layers sothat bending and vibration of the flexible display 100 can be providedsimultaneously or at a different timing. Such a combination can be usedin creating sound waves from the flexible display 100.

Some components of the flexible display 100 may make it difficult tobend the flexible display 100 along the bending line BL. Some of thecomponents, such as the support layer 108, the touch sensor layer 112,the polarization layer 110 and the like, may add more rigidity to theflexible display 100. Also, the thickness of such components shifts theneutral plane of the flexible display 100 and thus some of thecomponents may be subjected to greater bending stresses than othercomponents.

To facilitate easier bending and to enhance the reliability of theflexible display 100, the configuration of components in the bendportion 102 of the flexible display 100 differs from the central portion101 of the flexible display 100. Some of the components existing in thecentral portion 101 may not be disposed in the bend portions 102 of theflexible display 100, or may be provided in a different thickness. Thebend portion 102 may be free of the support layer 108, the polarizationlayer 110, the touch sensor layer 112, a color filter layer, and/orother components that may hinder bending of the flexible display 100.Such components may not be needed in the bend portion 102 if the bendportion 102 is to be hidden from the view or otherwise inaccessible tothe users of the flexible display 100.

Even if the second active area is provided in the bend portion 102 forproviding information to users, the second active area may not requiresome of these components depending on the usage and/or the type ofinformation provided by the second active area. For example, thepolarization layer 110 and/or color filter layer may not be needed inthe bend portion 102 when the second active area is used for simplyemitting colored light, displaying texts or simple graphical userinterfaces in a contrast color combination (e.g., black colored texts oricons in white background). Also, the bend portion 102 of the flexibledisplay 100 may be free of the touch sensor layer 112 if suchfunctionality is not needed in the bend portion 102. If desired, thebend portion 102 may be provided with a touch sensor layer 112 and/orthe layer of electro-active material even though the secondary activearea for displaying information is not provided in the bend portion 102.

Since the bend allowance section is most heavily affected by the bendingstress, various bending stress-reducing features are applied to thecomponents on the bend portion 102. To this end, some of the elements inthe central portion 101 may be absent in at least some part of the bendportion 102. The separation between the components in the centralportion 101 and the bend portion 102 may be created by selectivelyremoving the elements at the bend allowance section of the flexibledisplay 100 such that the bend allowance section is free of therespective elements.

As depicted in FIGS. 4 and 5, the support layer 108 in the centralportion 101 and the support layer 108 in the bend portion 102 can beseparated from each other by the absence of the support layer 108 at thebend allowance section 102 b. Instead of using the support layer 108attached to the base layer 106, a support member 116 with an end portioncan be positioned underside of the base layer 106 at the bend allowancesection. Various other components, for example the polarization layer110 and the touch sensor layer 112 and more, may also be absent from thebend allowance section of the flexible display 100. The removal of theelements may be done by cutting, wet etching, dry etching, scribing andbreaking, or other suitable material removal methods. Rather thancutting or otherwise removing an element, separate pieces of the elementmay be formed at the selective portions (e.g., central portion and thebend portion) to keep the bend allowance section free of such element.Rather than being entirely removed from the bend portion, some elementsmay be provided with a bending pattern along the bending lines and/orthe parts within the bend allowance section to reduce the bendingstress.

FIG. 5 illustrates a plane view and a cross-sectional view of bendingpatterns 300 in accordance with embodiments of the present application.The bending patterns 300 may be applied to some of the components. Thebending patterns 300 described above may be used in the support layer108, the polarization layer 110, the touch sensor layer 112 and variousother elements of the flexible display 100.

The flexible display 100 may utilize more than one type of bendingpatterns 300. It should be appreciated that a number of bending patternsand the types of the bending patterns 300 utilized by the components isnot limited. If desired, the depth of the patterns 300 may be deepenough to penetrate through the component entirely but penetrate onlypartially through the respective layer. A buffer layer positionedbetween the base layer 106 and the TFT as well as a passivation layercovering a conductive line may be provided with the bending pattern forreducing bending stress.

Referring back to FIG. 4, the support layer 108 may not be present atthe bend allowance section to facilitate bending of the base layer 106.Absent the support layer 108, however, the curvature at the bendallowance section may be easily altered by external force. To supportthe base layer 106 and maintain the curvature at the bend allowancesection, the flexible display 100 may also include a support member 116,which may also be referred to as a “mandrel.” The support member 116depicted in FIG. 4 has a body portion and an end portion. The base layer106 and the support member 116 are arranged so that that the end portionof the support member 116 is positioned at the underside of the baselayer 106 corresponding to the bend allowance section of the flexibledisplay 100.

In embodiments where a bend portion 102 is provided at an edge of theflexible display 100, the support member 116 can be provided at the edgeof the flexible display 100. In this setting, a part of the base layer106 may come around the end portion of the support member 116 and bepositioned at the underside the support member 116 as depicted in FIG.4. Various circuits and components in the inactive area of the flexibledisplay 100, such as drive ICs and interfaces for connectingchip-on-flex (COF) and printed circuit board (PCB), may be provided onthe base layer 106 that is positioned at the rear side of the flexibledisplay 100. In this way, even the components that are not flexible canbe placed under the active area of the flexible display 100.

The support member 116 can be formed of plastic material such aspolycarbonate (PC), polyimide (PI), polyethylene naphthalate (PEN),polyethylene terephthalate (PET), etc. The rigidity of the supportmember 116 formed of such plastic materials may be controlled by thethickness of the support member 116 and/or by providing additives forincreasing the rigidity. The support member 116 can be formed in adesired color (e.g., black, white, etc.). Further, the support member116 may also be formed of glass, ceramic, metal or other rigid materialsor combinations of aforementioned materials.

Size and shape of the end portion of the support member 116 can varydepending on the minimum curvature desired at the bend allowance sectionof the flexible display 100. In some embodiments, the thickness of theend portion and the thickness of the body portion may be substantiallythe same. In other embodiments, the body portion, which has a planarshape, may be thinner than the end portion of the support member 116.With a thinner profile at the body portion, the support member 116 cansupport the bend allowance section 102 b while avoiding furtherincreasing the thickness in the flexible display 100.

Since the support at the bend allowance section is provided by the endportion of the support member 116, the body portion extended toward thecentral portion 101 of the flexible display 100 needs not be extendedinto the active area. While the body portion can be extended under theactive area for various reasons, the length of the body portion from theend portion towards the opposite end is sufficient so long as the bodyportion provides enough surface region to secure the support member 116.

To secure the support member 116 in the flexible display 100, anadhesive layer 118 may be provided on the surface of the support member116. The adhesive layer 118 may include a pressure-sensitive adhesive, afoam-type adhesive, a liquid adhesive, a light-cured adhesive or anyother suitable adhesive material. In some embodiments, the adhesivelayer 118 can be formed of, or otherwise includes, a compressiblematerial and serve as a cushion for the parts bonded by the adhesivelayer 118. As an example, the constituent material of the adhesive layer118 may be compressible. The adhesive layer 118 may be formed ofmultiple layers, which includes a cushion layer (e.g., polyolefin foam)interposed between an upper and a lower layers of an adhesive material.

The adhesive layer 118 can be placed on at least one of the uppersurface and the lower surface of the body portion of the support member116. When the bend portion 102 of the flexible display 100 wraps aroundthe end portion of the support layer 116, an adhesive layer 118 can beprovided on both the lower surface (i.e., the surface facing the rearside) and the upper surface (i.e., the surface facing the front side) ofthe body portion. An adhesive layer 118 may be provided between thesurface of the end portion of the support member 116 and the innersurface of the base layer 106.

During bending, a part of the flexible display 100 on one side of thesupport member 116 may be pulled toward the support member 116, and thebase layer 106 may be damaged by the highest and the lowest edges of theend portion. As such, the heights of the adhesive layer 118 and thesupport layer 108 between the support member 116 and the base layer 106may be equal to or greater than the vertical distance between thehighest edge of the end portion and the surface of the body portionwhere the adhesive layer 118 is placed. In other words, the height ofthe space created by the thickness difference between the end portionand the body portion of the support member 116 may be equal to or lessthan the collective thickness of the support layer 108 and the adhesivelayer 118.

Depending on the shape of the support member 116, a thickness of theadhesive layer 118 on the upper and the lower surfaces of the bodyportion may be different. For instance, the body portion, which isthinner than the end portion, may not be at the center of the endportion of the support member 116. In such cases, the space on one sideof the support member 116 may be greater than the space on the oppositeside.

In another example, the lowest edge of the end portion may be providedinside of the bottom surface of the body portion such that the space isprovided only on one side of the body portion. In such cases, theadhesive layer 118 on one side of the body portion of the support member116 can be thicker than the one on the opposite side.

FIGS. 6A, 6B and 6C are simplified cross-sectional views showing anarrangement of elements in various embodiments of the flexible display100. In one suitable configuration, the thickness of the rounded endportion and the elongated body portion of the support member 116A may besubstantially the same as illustrated in FIG. 6A. Such a support member116A can be formed of the plastic materials. The support member 116A mayalso be formed of a folded thin sheet metal (e.g., SUS). In this case,the folded edge of the sheet metal can serve as the rounded end portionof the support member 116A. Even when a sheet metal is used to form thesupport member, the end portion can have greater thickness than the bodyportion. For instance, pressure can be applied on the part of the foldedmetal sheet for the body portion to make that portion thinner than thefolded edge.

In FIG. 6A, the adhesive layer 118A is illustrated as being applied onthe upper, the lower surface and the surface of the rounded end portionof the support member 116A. As the thickness of the support member 116Aat the rounded end portion and the body portion is about the same, thethickness of the adhesive layer 118A may have a substantially uniformthickness on the surface of the support member 116A. However, theadhesive layer 118A can be thinner and/or thicker at selective parts ofthe support member 116A.

In another suitable configuration, the elongated body portion of thesupport member 116 is thinner than its rounded end portion. In thisregard, the bottom surface of the body portion is in-line with thelowest edge of the end portion, providing a support member 116B with aflat bottom as depicted in FIG. 6B. In this configuration, the supportmembers 116B may be formed of one or a combination of aforementionedplastic materials (e.g., polycarbonate, etc.). Also, the adhesive layer118B provided on the upper surface of the body portion is thicker thanthe adhesive layer 118B provided on the bottom surface of the bodyportion of the support member 116B. The adhesive layer 118B on the uppersurface of the body portion may include a cushion layer described abovewhile the adhesive layer 118B on the lower surface does not.

In yet another suitable configuration shown in FIG. 6C, neither the topnor the bottom surfaces of the body portion of the support member 116Cis in-line with the highest/lowest edges of the rounded portion. Thesupport members 116C may be formed of one or a combination ofaforementioned plastic materials (e.g., polycarbonate, etc.). In thisexample, the body portion is off-centered (i.e., closer to the lowestedge of the rounded portion), and the adhesive layer 118C on the uppersurface of the body portion is thicker than the adhesive layer 118C onthe lower surface. The adhesive layer 118C on the upper surface of thebody portion may include a cushion layer described above while theadhesive layer 118C on the lower surface does not.

In the configurations depicted in FIGS. 6A-6C, the support layer 108 onthe upper side of the support member 116 can be extended further outtoward the bend allowance section than the encapsulation there above. Inother words, a part of the base layer 106 toward the bend allowancesection is not covered by the encapsulation, but provided with thesupport layer 108 thereunder. The extra length of the support layer 108can help maintain a curvature in the bend allowance section. The edge ofthe support layer 108 under the support member 116 may be shifted awayfrom the bend allowance section. In some embodiments, the edge of thesupport layer 108 toward the bend allowance section can be provided witha flange, which extends even further out toward the bend allowancesection as shown in FIG. 6A. In one example, the flange may be made bycutting, or otherwise patterning, the support layer 108 to have atapered edge. In another example, the flange can be provided by stackingat least two support layers with their edges shifted from each other.While omitted in FIGS. 6B and 6C, the flange can be provided in thoseembodiments as well.

It should be appreciated that the configurations described above inreference to FIGS. 6A-6C are merely illustrative. Adhesive layers havingthe same thickness can be provided on the upper and the lower surfacesof the support member regardless of the position of the body portion.Further, adhesive layers on the upper surface or the lower surface ofthe support member can include a cushion layer.

Several conductive lines are included in the flexible display 100 forelectrical interconnections between various components therein. Thecircuits fabricated in the active area and inactive area may transmitvarious signals via one or more conductive lines to provide a number offunctionalities in the flexible display 100. Some conductive lines maybe used to provide interconnections between the circuits and/or othercomponents in the central portion and the bend portion of the flexibledisplay 100.

As used herein, the term conductive lines broadly refers to a trace ofconductive path for transmitting any type of electrical signals, powerand/or voltages from one point to another point in the flexible display100. As such, conductive lines may include source/drain electrodes ofthe TFTs as well as the gate lines/data lines used in transmittingsignals from some of the display driving circuits (e.g., gate driver,data driver) in the inactive area to the pixel circuits in the activearea. Likewise, some conductive lines, such as the touch sensorelectrodes, pressure sensor electrodes and/or fingerprint sensorelectrodes may provide signals for sensing touch input or recognizingfingerprints on the flexible display 100. Furthermore, conductive linescan provide interconnections between components of the active area inthe central portion and components of the second active area in the bendportion of the flexible display 100.

Conductive lines in a flexible display 100 should be carefully designedto meet various electrical and non-electrical requirements. Forinstance, a conductive line may have a specific minimum electricalresistance level, which may vary depending on the type of signals to betransmitted via the conductive line. Some conductive lines may be routedfrom the substantially flat portion to the bend portion of the flexibledisplay 100. Such conductive lines should exhibit sufficient flexibilityto maintain its mechanical and electrical robustness. Some conductivelines of the flexible display 100 may have a multi-layered structure.

FIGS. 7A and 7B each illustrates stack structure of the multi-layeredconductive line. Referring to FIG. 7A, the conductive line 120 has amulti-layered structure in which the primary conductive layer 122 issandwiched between the secondary conductive layers 124. The primaryconductive layer 122 may be formed of material with a lower electricalresistance than that of the secondary conductive layer 124. Non-limitingexamples of the materials for the primary conductive layer 122 includescopper, aluminum, transparent conductive oxide, or other flexibleconductors.

The secondary conductive layer 124 should be formed of conductivematerial that exhibits sufficiently low ohmic contact resistance whenformed in a stack over the primary conductive layer 122. Low ohmiccontact resistance between the conductive layers is not the only factorin the selection of materials for the conductive layers in themulti-layered conductive line 120. While meeting the stringentelectrical and thermal requirements (e.g., resistance, heat generation,etc.), the materials of the conductive line 120 should also satisfy theminimum mechanical stress requirement (e.g., Young's modulus). That is,both the primary conductive layer 122 and the secondary conductive layer124 should be formed of materials exhibiting sufficient flexibility.

Accordingly, in some embodiments, at least some of the conductive lines120 of the flexible display 100 may be formed with two or more of layersselected from aluminum (Al), titanium (Ti), molybdenum (Mo), Copper (Cu)layers. Examples of such combination include an aluminum layersandwiched between titanium layers (Ti/Al/Ti), an aluminum layersandwiched between upper and lower molybdenum layers (Mo/Al/Mo), acopper layer sandwiched between titanium layers (Ti/Cu/Ti) and a copperlayer sandwiched between upper and lower molybdenum layers (Mo/Cu/Mo).Other conductive materials can be used for the primary/secondaryconductive layers.

Electronic device employing the flexible display 100, for instance awearable electronic device or a water submergible electronic device, mayexpose the flexible display 100 in a humid environment. In some cases,moist can reach the conductive line 120. Dissimilar metals and alloyshave different electrode potentials, and when two or more come intocontact in an electrolyte, one metal acts as anode and the other ascathode. The electro-potential difference between the dissimilar metalsaccelerates corrosion on the anode member of the galvanic couple, whichwould be the primary conductive layer 122 in the multi-layeredconductive line 120 (e.g., Al layer in the Ti/Al/Ti stack). The anodemetal dissolves into the electrolyte, and deposit collects on thecathodic metal.

When using a multi-layered conductive line 120 described above, anysurface that exposes both the primary conductive layer 122 and thesecondary conductive layer 124 may become a galvanic corrosioninitiation point. Accordingly, in some embodiments of the flexibledisplay 100, at least some conductive lines 120 is provided with astructure in which the outer surface of the primary conductive layer 122is surrounded by the secondary conductive layer 124 as shown in FIG. 7B.Such a configuration hinders the electrolyte from being in contact withboth the primary conductive layer 122 and the secondary conductive layer124, thereby reducing the loss of the primary conductive layer 122 bygalvanic corrosion.

Such a multi-layered conductive lines 120 can be created by depositingthe material for the primary conductive layer 122 (e.g., Al) over thesecondary conductive layer 124 (e.g., Ti). Here, the secondaryconductive layer 124 underneath the primary conductive layer 122 mayhave greater width. Etch resist material is formed over the stack ofthese two layers and etched (e.g., dry etch, wet etch, etc.) to form theconductive line in a desired trace. After striping the etch resistancematerial, secondary conductive layer 124 (i.e., Ti) is deposited overthe patterned structure (i.e., Ti/Al). The width of the secondaryconductive layer 124 deposited over the primary conductive layer 122 maybe greater than the width of the primary conductive layer 122 to coverthe outer surface of the primary conductive layer 122. Another round ofetching and striping of the etch resistance material is performed toform a multi-layered conductive line in a desired conductive line tracedesign. It should be understood that the multi-layered conductive lineformation processes described above are merely an example. Accordingly,some processes may be added and/or skipped in making a multi-layeredconductive line.

A trace design of a conductive line is an important factor, which canaffect the conductive line's electrical and mechanical properties. Tomeet the electrical and mechanical requirements, some portion of aconductive line may be configured differently from another portion ofthe conductive line. As such, a portion of a conductive line at or nearthe bend allowance section of the flexible display 100 may be providedwith several features for bending stress management.

Bending stress management of the insulation layers near the conductiveline is just as important as managing the strain of the conductive lineitself. Various insulation layers, such as the buffer layer 126, thepassivation layer 128, a gate insulation layer (GI layer) and aninterlayer dielectric layer (ILD layer) positioned below and/or abovethe conductive line 120 may include a layer of inorganic materials.Layers that are formed of inorganic material, for instance a siliconoxide layer and a silicon nitride layer, are generally more prone tocracks than the metal layers of the conductive line. Even when theconductive lines have a sufficient flexibility to cope with the bendingstress without a crack, some of the cracks initiated from the insulationlayer can propagate into the conductive lines and create spots of poorelectrical contacts in the flexible display 100.

As a trace design for reducing bending stress on a conductive line, someof the insulation layers above and/or below the layer of conductive line120 may be patterned to reduce the chance of generating cracks. Variousinsulation layer patterning techniques, such as wet etching and/or dryetching processes, can be used to form a trace of insulation layer thatcorresponds to the trace of a conductive line. Lack of insulation layer,especially the inorganic material based insulation layer around thetrace of a conductive line not only lowers the chance of crackgeneration, but it also cuts off the path for a crack propagation. Forconvenience of explanation, a trace of conductive line 120 and a traceof insulation layers covering at least some part of the conductive line120 are collectively referred to as the “wire trace” in the followingdescription.

As mentioned, a trace design for the conductive line and the insulationlayer covering the conductive line plays an important role in increasingthe robustness of the wire trace. Numerous parameters, ranging from athickness and a width of a wire trace to a fan-out angle of a wire tracesegment with respect to the bending direction of the flexible display100, are associated with the wire trace design. In addition to theaforementioned parameters, various other parameters regarding theconductive line 120 and the insulation layer trace are specificallytailored based on the placement and the orientation of the wire tracewithin embodiments of the flexible display 100.

Strain on a wire trace from the bending stress will be greater as thedirection in which the wire trace extends is more aligned with thetangent vector of the curvature. In other words, a wire trace willwithstand better against the bending stress if the length of a wiretrace segment being parallel to the tangent vector of the curvature isreduced. No matter which direction the wire trace is extended to, therewill always be a portion in the wire trace that is measurable in thebending direction. However, a length for each continuous measurableportion (i.e., a segment) being aligned parallel to the bendingdirection can be reduced by employing a strain-reducing trace design inthe wire trace.

FIG. 8 illustrates some of the strain-reducing trace designs. Any one ormore of a sign-wave, a square-wave, a serpentine, a saw-toothed and aslanted line trace designs illustrated in FIG. 8 can be used for wiretraces of the flexible display 100. Employing such a strain-reducingtrace design increases the portion of the wire trace arranged in aslanted orientation with respect to the tangent vector of the curvature.This, in turn, limits the length of the wire trace segment extending ina straight line parallel to the bending direction.

Since the cracks in the wire trace by bending of the flexible displaygenerally initiate from an inorganic insulation layer, the length of theinsulation layer trace being aligned with the tangent vector of thecurvature should also be minimized. In the single line strain-reducingdesigns, the width and the shape of the conductive line trace as well asthe width of the patterned inorganic insulation layers interfacing withthe surface of the conductive line trace should be kept minimal.

The strain-reducing trace designs illustrated in FIG. 8 are merelyexemplary, and other trace designs for reducing the length of a wiretrace segment parallel to the bending direction may be used in variousembodiments of the flexible display 100. Further, some wire traces mayadopt different strain-reducing trace design from other wire traces in aflexible display 100 depending on their electrical and/or mechanicalrequirements. For instance, a strain-reducing trace design used for adata signal line may be different from a strain-reducing trace designused for a power line.

To further improve robustness, a wire trace may employ a trace design inwhich the wire trace repeatedly splits and converges back in a certaininterval. In other words, a wire trace includes at least two sub-tracesarranged to form a trace design resembling a chain with a series ofconnected links. The angles of split and merge define the shape of eachlink, which allows to limit the length of the wire trace segmentmeasurable in straight line parallel to the bending direction.

Referring to FIG. 9A, the conductive line 120 includes sub-trace A andsub-trace B, which are split away from each other and merge back at eachjoint X. Between the first joint X(1) and the second joint X(2), a partof the sub-trace A is extended for a predetermined distance in a firstdirection angled away from the tangent vector of the curvature, andanother part of the sub-trace A is extended in a second direction. Thesub-trace B is arranged in a similar manner as the sub-trace A, but in amirrored orientation in reference to the tangent vector of thecurvature. The distances and directions in which the sub-traces arearranged between the two adjacent joints X define the shape and the sizeof the link in the chain as well as the open area surrounded by thesub-traces. In this example, the shape of the conductive line 120between the joint X(1) and X(2) i.e., link has a diamond shape with anopen area surrounded by the sub-trace A and the sub-trace B. Withadditional joints X, the conductive line 120 forms a chain of diamondshaped links, and thus the trace design may be referred to as thediamond trace design.

Compare to the non-split strain-reducing trace designs shown in FIG. 8,the strain-reducing trace design shown in FIG. 9A can providesignificant advantages in terms of electrical property. For instance,the wire trace provided with the split/merge trace design can providemuch lower electrical resistance than the wire traces employing themountain trace design, the sign-wave trace designs or other single linestrain-reducing trace designs of FIG. 8. In addition, sub-traces canserve as a backup electrical pathway in case one of the sub-traces isdamaged or severed by cracks.

The insulation layers covering the surfaces of the conductive line 120is also patterned in a trace design corresponding to the trace design ofthe conductive line 120. As such, the open area surrounded by thesub-trace A and the sub-trace B is free of the inorganic insulationlayer(s), or has thinner inorganic insulation layer(s) than the areasunder and/or above the trace of conductive line 120. As such, the lengthof the insulation layer trace measurable in straight line parallel tothe bending direction can be limited to reduce the chance of crackinitiation and propagation.

Various additional factors must be considered for the strain-reducingtrace designs based on a plurality of sub-traces. The split/merge anglesand the length of each sub-traces between two adjacent joints X shouldprovide an offset for the inorganic insulation layer at the joints X andat the outer corners where the sub-trace changes its direction betweentwo adjacent joints X. To put it in another way, the open area, which issurrounded by the split sub-traces between two joints X of the wiretrace, should have a size and a shape to minimize the length in which aninorganic insulation layer trace of the wire trace extending parallel tothe bending direction.

In the diamond trace design depicted in FIG. 9A, the buffer layer 126and the passivation layer 128 covering the trace of the conductive line120 are patterned with a predetermined margin from the outer trace(i.e., outer edge) of the conductive line 120. Other than the insulationlayers with the predetermined margin remaining to cover the conductiveline 120, the open area surrounded by the sub-traces A and B, which isdenoted as FA2, is free of the insulation layers. As such, a trace ofinsulation layers is formed in accordance with the trace design of theconductive line 120. The length of the open area without the insulationlayers measured in orthogonal direction from the bending direction isgreater than the width of the inorganic insulation layer trace at thejoint X measured in the same direction. In this setting, the open areaFA2 surrounded by the sub-traces A and B as well as the area next to thejoint X can be free of the inorganic insulation layers, or otherwiseprovided with a reduced number of inorganic insulation layers.

Referring to FIG. 9A, the insulation layer free area FA1 prevents theinsulation layer of the sub-trace A and the sub-trace B between the twojoints X(1) and X(2) to be extended in a continuous straight line.Similarly, the insulation layer free area FA2 prevents the insulationlayer between the two joints X(1) and X(2) to be extended in acontinuous straight line. Accordingly, the length of each segment of theinsulation layer trace being aligned to the tangent vector of thecurvature is minimized. Further reduction in the length of each segmentof the insulation layer trace aligned to the tangent vector of thecurvature can be obtained by reducing the width of the conductive line120 and the margin of the insulation layer beyond the edge of conductiveline 120.

It should be noted that the amount of reduction in the width ofconductive line 120 is limited with the single line strain-reducingtrace designs depicted in FIG. 8 because the reduction of conductiveline width can make its electrical resistance too high for itsparticular use within the flexible display 100. With the split/mergetrace design of FIG. 9A, however, the width of the conductive line 120and the insulation layer trace can be reduced while providing sufficientelectrical property.

Greater split/merge angle of the sub-traces with respect to the bendingdirection may allow to reduce the lengths of the conductive line 120 andthe insulation layer trace extending along the tangent vector of thecurvature to a greater extent. Accordingly, a lower chance of crackinitiation may be afforded in the wire trace by selectively increasingthe split/merge angle of sub-traces at high bending stress regions.

It should be noted that the split angle of the sub-traces can affect thedistance between the two adjacent joints X in the diamond trace design.The distance between the joints X need not be uniform throughout theentire wire trace. The intervals at which the trace splits and mergescan vary within a single trace of wire based on the level of bendingstress exerted on the parts of the wire trace. The distance between thejoints X may be progressively shortened down for the parts of the wiretrace towards the area of the flexible display 100 subjected to higherbending stress (e.g., area having smaller bend radius, area havinglarger bend angle). Conversely, the distances between the joints X canprogressively widen out towards the area subjected to lower bendingstress.

Even with the strain-reducing trace design, the inevitable bendingstress remains at certain points of the trace (i.e., stress point). Thelocation of stress point is largely dependent on the shape of the traceas well as the bending direction. It follows that, for a given bendingdirection, the wire trace can be designed such that the remainingbending stress would concentrate at the desired parts of the wire trace.Knowing the location of the stress point in the wire trace, a crackresistance area can be provided to the stress point to make the wiretrace last longer against the bending stress.

Referring back to FIG. 9A, when a wire trace having the diamond tracedesign is bent in the bending direction, the bending stress tends tofocus at the angled corners (i.e., the vertexes of each diamond shapedlink), which are denoted as the stress point A and stress point B. Assuch, cracks tend to initiate and grow between the inner and outer edgesof the wire trace. For instance, at the stress points A, a crack mayinitiate from the inner trace line 120(IN) and grow toward the outertrace line 120(OUT). Similarly, a crack may initiate from the outer wiretrace line 120(OUT) and grow toward the inner trace line 120(IN) at thestress points B.

Accordingly, the width of the conductive line 120 at the stress points Acan be selectively increased to serve as the crack resistance area. Asdepicted in FIG. 9A, the widths (W_(A), W_(B)) of the conductive line120 at the stress points A and B, which are measured in the directionperpendicular to the bending direction, may be longer than the width (W)of the conductive line 120 at the parts between the stress points A andB. The extra width at the stress points can make the conductive line 120held out longer before a complete severance in the conductive line 120occurs by the growth of a crack at the stress points.

The length for the continuous portion of the insulation layer tracebeing aligned to the bending direction should be kept minimal.Increasing the width of the conductive line 120 at the stress points Aand B may necessitate increase in the width of the insulation layertrace at the respective area, which results in lengthening theinsulation layer trace being aligned parallel to the bending direction.

Accordingly, in some embodiments, the width of the conductive line 120measured in the direction perpendicular to the tangent vector of thecurvature at the stress points A ranges from about 2.5 um to about 8 um,more preferably, from about 3.5 um to about 6 um, more preferably fromabout 4.5 um to about 8.5 um, and more preferably at about 4.0 um. Thewidth of the conductive line 120 at the stress points B should also bemaintained in the similar manner as the width of the conductive line 120at the stress points A. As such, the width of the conductive line 120 atthe stress points B may range from about 2.5 um to about 8 um, morepreferably, from about 3.5 um to about 6 um, more preferably from about4.5 um to about 8.5 um, and more preferably at about 4.0 um. Since thesub-trace A and the sub-trace B merges at the stress point B, the widthof the conductive line 120 at the stress points B may be longer thanwidth at the stress points A.

In some embodiments, one of the inner trace line 120(IN) and the outertrace line 120(OUT) may not be as sharply angled as the other trace lineat the stress points A to minimize the chance of crack initiating fromboth sides. In the embodiment depicted in FIG. 9A, the inner trace line120(IN) is more sharply angled than the outer trace line 120(OUT) at thestress points A. However, in some other embodiments, the outer traceline 120(OUT) may be more sharply angled than the inner trace line120(IN) at the stress points A. In both cases, the less sharply angledtrace line can be more rounded rather than being a straight line as theouter trace line 120(OUT) depicted in FIG. 9A. Further, both the innertrace line 120(IN) and the outer trace line 120(OUT) at the stresspoints A can be rounded.

The wire trace may split into additional number of sub-traces, resultingseries of links arranged in a grid-like configuration. As an example, awire trace can be configured as a web of diamond trace shapes asillustrated in FIG. 9B. Such a trace design is particularly useful for awire trace that transmit a common signal to multiple points or for awire trace that require a very low electrical resistance. For example, aVSS line and a VDD line in the flexible display 100 may have thegrid-like trace design, especially if such lines are arranged to crossover a bend allowance section. Neither the number of sub-traces nor theshapes of the sub-traces of the grid-like trace design are particularlylimited as the design depicted in FIG. 9B.

In some embodiments, the grid width can be reduced or increased inbetween two ends within the flexible display 100. Also, the grid-likewire trace shown in FIG. 9B can converge back to form the diamond traceshown in FIG. 9A or to form a non-split strain-reducing trace design. Insome cases, the size of each diamond-shaped trace of a grid-like wiretrace may be larger than the size of each diamond-shaped trace of adiamond-chain trace to reduce the resistance.

Due to the portions angled away from the bending direction, a wire tracewith a strain-reducing trace design may necessitate a larger routingarea within the flexible display 100. In embodiments where an inactivearea at the edge of the flexible display 100 is bent, the increase inthe routing area for accommodating the wire traces can actually increasethe size of the inactive area to be hidden under a masking.

Accordingly, wire traces applied with a strain-reducing trace design maybe arranged to facilitate tight spacing between adjacent wire traces.For instance, two adjacent wire traces with a strain-reducing tracedesign may each include a non-linear section, which would have a convexside and a concave side. The two adjacent wire traces can be arranged inthe flexible display such that the convex side of the non-linear sectionin the first wire trace is positioned next to the concave side thenon-linear section in the second wire trace. Since the spacing betweenthe two adjacent wire traces is limited by the shape and the size of thewire traces, the non-linear section in the strain-reducing trace designof the first wire trace may be larger than the non-linear section in thestrain-reducing trace design of the second wire trace. One of the firstwire trace and the second wire trace may have a differentstrain-reducing trace design to better accommodate the non-linearsection of the other wire trace.

In some instances, two or more wire traces arranged next to each othermay each be applied with a strain-reducing trace design, and each of thewire traces may have a plurality of indented sections and distendedsections. In such cases, the wire traces can be arranged such that thedistended section of one of the wire traces to be positioned next to theindented sections of the adjacent wire trace.

FIG. 10 illustrates an arrangement of multiple wire traces, each havingthe diamond trace design described above. The split of the sub-traceswidens the layout of the wire trace to create the distended section,whereas merging of the sub-traces narrows the layout of the wire traceto create the indented section. Accordingly, in terms of its layout, theindented section of the wire trace is at the joint X, whereas thedistended section of the wire trace is at the point where thesplit/merge angles of the sub-traces change between two adjacent jointsX.

As shown in FIG. 10, position of the joints X in a first wire trace andthe joints X in a second wire trace are arranged in a staggeredconfiguration. In this arrangement, the vertexes of the diamond shapedlink at the distended section in the first wire trace are positionednext to the joints X at the indented sections of the adjacent wiretraces. Such a staggered arrangement of the wire traces may help inlowering the electrical noises on the wire traces due to close proximitybetween the wire traces, and thus the distance between the wire tracescan be reduced. Even a tight spacing between the wire traces may bepossible by arranging the distended section of a wire trace to bepositioned closer toward the indented section of the adjacent wiretrace. For instance, the vertexes at the wide parts of one wire race canbe placed in the open area FA1, which is created by the split/mergeangle and the length of the sub-trace in the adjacent wire trace. Assuch, the staggered arrangement allows to maintain certain minimaldistance between the wire traces while reducing the amount of spacetaken up by the wire traces.

FIGS. 11A and 11B illustrate schematic cross-sectional views of tracedesigns usable for wire traces in a flexible display according toembodiments of the present disclosure.

It should be noted that cracks primarily initiate from the inorganicinsulation layers. Accordingly, propagation of cracks can be suppressedby selectively removing inorganic insulation layers from the areas proneto cracks. To achieve this, one or more inorganic insulation layersand/or stack of insulation layers including a layer of inorganicmaterial can be selectively etched away at various parts of the flexibledisplay 100.

For example, the insulation layer under the conductive line 120 can beetched away. The insulation layer under the conductive line 120 may bethe buffer layer 126, which may include one or more layers of inorganicmaterial layers. The buffer layer 126 may be formed of one or morelayers of a SiNx layer and a SiO2 layer. In one suitable configuration,the buffer layer 126 may be formed of alternating stacks of a SiNx layerand a SiO2 layer. The buffer layer 126 is disposed on the base layer106, but under the TFT.

To facilitate easier bending of the flexible display 100, a part of thebuffer layer 126 may etched away in the bend portion of the flexibledisplay 100. Accordingly, the buffer layer 126 formed on thesubstantially flat portion of the base layer 106 may be thicker than thebuffer layer 126 over the bend portion of the base layer 106. When thebuffer layer 126 is formed in a stack of multiple sub-layers, the bufferlayer 126 in the substantially flat portion of the flexible display 100may include one or more additional sub-layers than the buffer layer inthe bend portion of the flexible display 100.

For example, the buffer layer 126 in the substantially flat portion mayinclude multiple stacks of a SiNx layer and a SiO2 layer, and the bufferlayer 126 in the bend portion includes a single stack of a SiNx layerand a SiO2 layer. It is also possible to have only a single layer ofeither a SiNx layer or a SiO2 layer in some part of the bend portion. Inone configuration, each SiNx layer and SiO2 layer in the buffer layer126 may have a thickness of about 1000 Å. As such, the thickness of thebuffer layer 126 in the bend portion of the flexible display may rangefrom about 100 Å. to about 2000 Å.

In the substantially flat portion of the flexible display 100,additional layer of inorganic layer may be provided immediately belowthe semiconductor layer of the TFT, which may be referred to as theactive buffer. In some embodiments, an inorganic layer, which is mostclosely positioned under the active layer of the TFT, may be muchthicker than the individual inorganic layers of the buffer layer 126.

The buffer layer 126 in the bend allowance section may be etched evenfurther to expose the base layer 106 while leaving the buffer layer 126intact under the conductive line 120. In other words, a recessed areaand a protruded area are provided in the bend portion of the flexibledisplay 100. The protruded area includes the buffer layer 126 providedon the base layer 106, whereas the recessed area has the base layer 106exposed without the buffer layer 126 disposed thereon.

In one configuration shown in FIG. 11A, the conductive line 120 ispositioned on the protruded area, and the passivation layer 128 ispositioned over the conductive line 120 on the protruded area. Althoughthe passivation layer 128 may not be deposited over the recessed area,the passivation layer 128 can be removed from the recessed area by a dryetch or a wet etch process. As such, the recessed area can besubstantially free of the passivation layer 128. When etching thepassivation layer 128 from the recessed area, part of the base layer 106can be etched as well. Accordingly, the thickness of the base layer 106at the recessed area can be lower than that of the base layer 106elsewhere in the flexible display 100. When the buffer layer 126 isetched away as shown in FIG. 11A, propagation of crack from one part ofthe buffer 126 to another part of the buffer layer 126 can be hinderedby the space in the recessed area. Similarly, propagation of cracks bythe passivation layer 128 is also hindered by the space of the recessedarea. Accordingly, damage to the conductive line 120 by propagation ofcracks can be reduced.

In another configuration shown in FIG. 11B, the recessed area includesthe base layer 106 that is etched to a certain depth, and the conductiveline 120 is deposited on the base layer 106 of the recessed area. Inthis setting, the portion of the conductive line 120 is disposed withinthe base layer 106. Some part of the conductive line 120 is alsodeposited on a part of the buffer layer 126 that is provided in theprotruded area. A passivation layer 128 can be deposited over theconductive line 120, and then etched away from the recessed area toexpose the conductive line 120 in the recessed area.

Accordingly, the passivation layer 128 remains on the conductive line120 positioned on the protruded area. In this configuration, thepassivation layer 128 remaining on the buffer layer 126 can inhibitgalvanic corrosion as it covers the cross-sectional side surface of themulti-layered conductive line 120. While cracks generated from thebuffer layer 126 may penetrate to the conductive line 120 on the wall ofhollow space in the buffer layer 126, the cracks may be prevented fromreaching the part of the conductive line 120 positioned within the baselayer 106.

When the conductive line 120 has the multi-layered structure discussedabove, the part of the conductive line 120 in the recessed area needsnot be covered by the passivation layer 128. With the passivation layer128 removed from the surface of the conductive line 120 in the recessedarea, crack propagation from the passivation layer 128 can also beprevented. Further, galvanic corrosion generally starts from the edge ofthe conductive line 120 on the buffer layer, and thus the passivationlayer 128 covering the edge of the conductive line 120 on the buffer 126may not be needed if the distance between the conductive line 120 on thebuffer layer 126 and the conductive line 120 in the base layer 106 issufficiently spaced apart from each other. The configurations shown inFIGS. 11A and 11B may be used for the wire traces in the bend allowancesection with the strain-reducing trace patterns of FIGS. 8, 9A and 9B.In addition to the bend allowance section, in some embodiments, thepatterned insulation layer may also be provided in the routing areabetween the active area and the bend allowance section as well as therouting area between the COF bonding area and the bend portion.

Further, the patterned insulation layer described above can be providedin the active area. However, removal of inorganic insulation layers nearthe TFTs of the flexible display 100 may affect the electricalcharacteristic of components in the flexible display 100. For instance,undesired threshold voltage shift of TFTs may result when some part ofthe buffer layer 126 is removed. In order to maintain the stability ofthe TFTs, an additional shield metal layer can be formed under thesemiconductor layer of the TFTs. The shield metal layer may be under thebuffer layer 126 or interposed between the inorganic layers of thebuffer layer 126. In some embodiments, the shield metal layer may beelectrically connected to the source electrode or gate electrode of theTFTs.

In addition to the patterning of insulation layers in various parts ofthe flexible display 100, other structural elements can be removed orsimplified in some areas of the flexible display 100 to facilitatebending. For example, the touch sensor layer 112, the polarization layer110 and the likes may be absent in the bend allowance section of theflexible display 100. Absence or simplification of these elements wouldcreate a number of uneven surfaces where the wire trace may need tocross.

When a wire trace is laid over such an uneven surface, some parts of thewire trace may be placed on a different plane level from another partsof the wire trace. As the parts are on different plane levels, theamount and direction of bending stress and the strain resulting from thebending stress can differ even among the parts of the wire trace. Toaccommodate the difference, a strain-reducing trace design for the wiretraces can include a modified trace design for the portion of the wiretrace on the uneven surfaces.

FIG. 12A is an enlarged cross-sectional view showing a backplaneconfiguration for a flexible display 100, in which several insulationlayers are removed from the bend portion to facilitate more reliablebending, according to an embodiment of the present disclosure.

Several organic and inorganic layers may be formed in between the baselayer 106 and the OLED element layer 150. In this particular example,alternating stacks of SiNx and SiO2 layers can be disposed on the baselayer 106 to serve as the buffer layer 126. The semiconductor layer 151of a TFT may be sandwiched by an active-buffer layer 127 and a gateinsulation layer 152 that are formed of SiO2 layer. The gate 152 of theTFT is disposed on the gate insulation layer 152, and metal layer (samemetal with the source/drain of the TFT) having the multi-layeredstructure as discussed above is sandwiched between the ILD 154 and apassivation layer 128. Here, the ILD 154 may be formed of a stack ofSiNx and SiO2, and the passivation layer 128 is formed of SiNx. Then, aplanarization layer is disposed over the passivation layer 128 so thatthe anode for the OLED can be disposed thereon.

As mentioned above, use of the strain-reducing trace design is not justlimited to the part of the wire traces within the bend portion. Also,the strain-reducing trace design can be applied to the part of the wiretraces in the routing areas outside the bend allowance section. Usingthe strain-reducing trace design for the wire trace in such routing areacan afford increased protection to the wire trace against the bendingstress.

In the routing area, however, several layers of organic and/or inorganicmaterial layers between the base layer 106 and the OLED element layer150 may be absent to facilitate bending of the flexible display 100.Such organic and/or inorganic layers, including but not limited to theILD 154, the gate insulation layer 152, buffer layer 126, 127,passivation layer 128, planarization layer, etc. may not be present inthe bend portion of the flexible display 100. Some of these layers mayhave been removed from the area by several etching processes.

By way of example, several insulation layers on the buffer layer 126 maybe etched by a first etch process EB1, which is followed by the secondetch process EB2 that etches away the active buffer layer 127 and a partof the buffer layer 126 (e.g., a stack of a SiNx layer and a SiO2layer). These etching processes create multiple stepped regions as shownin FIG. 12A, with one or more of vertically sloped surfaces andhorizontally leveled surfaces, where the conductive line is disposedthereon. The conductive line laid over the vertically sloped surfacesand horizontally leveled surfaces would have several bent spots, such asa stepped region between a high-leveled surface and a low-leveledsurface.

When bending the flexible display 100 in the bending direction, the wiretrace may experience more strain at or near the stepped region. Numeroustests and experiments indicate that the chance of a crack is especiallyhigher in the wire trace crossing over the stepped region between theEB1 area and the EB2 area. Accordingly, in some embodiments, thestrain-reducing trace design for the wire trace has a reinforced portionat or near the stepped region between a high-leveled surface and alow-leveled surface provided by insulation layers of the flexibledisplay.

In the example shown in FIG. 12B, the wire trace has a simple straightline trace at its both ends. However, the part of the conductive line120 that crosses over the bent areas EB1 and EB2 is reinforced with amodified trace design. At the modified portion, the conductive line 120having a wider width with extra width W_(R) is provided to ensure theperseveration of the conductive line 120 even if cracks initiate fromthe insulation layer near EB1 and EB2 areas. The distance D_(R) in whichprovided in the modified trace design depends on the thickness of theinsulation layers etched by the etch processes as well as the distancebetween the first leveled surface (e.g., plane level at EB1) and asecond leveled surface (e.g., plane level at EB2).

It should be appreciated that the strain-reducing trace design of thewire trace applied with the modified portion is not limited to thestrain-reducing trace design depicted in FIG. 12B. Various embodimentsof the strain-reducing trace design can include a modified trace designfor the portion of the wire trace corresponding to the stepped areas oftwo differently leveled surfaces.

While this may not always be the case, the routing areas adjacent to thebend allowance section may be the substantially flat portions of theflexible display 100. In such cases, the EB1 and EB2 areas would bepositioned at or just outside start of the bend allowance section in thebend portion, and the wire trace may be provided with the reinforcedportion in its trace design.

The increased width W_(R) of the reinforced conductive line 120 portionmay serve its purpose well at or near the beginning and the end of thebend allowance section where the curvature is relatively small. Thewider width W_(R) of the wire trace and the length in which the modifiedtrace portion is applied in the wire trace can increase the length ofthe wire trace that is aligned parallel to the bending direction. Thiswould make the wire trace harder to hold out against the bending stressat the region with greater bend radius.

For this reason, the distance D_(R) in which the reinforced portion isprovided should be limited such that the reinforced conductive lineportion does not extend too much toward the bend allowance section.Accordingly, the distance D_(R) of the reinforced conductive lineportion may be limited such that the trace design of the reinforcedconductive line portion does not extend beyond the bend allowancesection where it is bent more than a predetermined threshold bend angle.By way of an example, the reinforced conductive line portion may notextend beyond the point where it is 30° curved away from the tangentplane of the curvature. The threshold bend angle may be less than 20°,for example 10°, and more preferably less than 7.

The wire trace, which is provided with the reinforced portion at thestepped areas, may extend across the bend allowance section and routedto pads for COF or other components of the flexible display 100. In suchinstances, additional stepped region (similar to EB1 and EB2) may existat or near the opposite end of the bend allowance section. Theconductive line at or near such bent spots may be reinforced in thesimilar manner as the modified portion of the wire trace at the oppositeend as shown in FIG. 12B. If desired, the reinforced conductive lineportion at or near the stepped regions at the opposite ends of the bendallowance section may have a different shape as depicted in FIG. 12B.

FIGS. 13A to 13C are views illustrating a protective coating layer usedfor a flexible display according to an embodiment of the presentdisclosure.

When several layers are not provided in a bend portion of the flexibledisplay 100, a passivation layer may be used for conductive lines,specifically, wire traces in the bend allowance section. Further, sincean inorganic insulation layers may be etched at the bend portion of theflexible display 100, conductive lines of the bend portion may besusceptible to moisture or other foreign matters. Specifically, variouspads and conductive lines for testing parts during the manufacturingprocess of the flexible display 100 may be chamfered, which may remain aconductive line extending to an grooved edge of the flexible display100. The conductive lines may be easily corroded by moisture and thecorrosion may expand to neighboring conductive lines. Accordingly, aprotective coating layer which may also be referred to as a“micro-coating layer” may be provided on the conductive line and/or thewire trace of the bend portion.

The protective coating layer 132 may be coated on a bend allowancesection with a thickness which is determined to adjust a neutral planeof the flexible display 100 in the bend portion. More specifically, athickness added to the protective coating layer 132 in the bend portionmay move the plane of the conductive line and/or the wire trace to becloser to the neutral plane.

In some embodiments, in a region between a barrier film 104 and aprinted circuit board 134, a thickness of the micro-coating layer 132measured from a surface of the base layer 106 may be substantially thesame as a thickness (from the base layer 106 to an upper surface of thebarrier film 104) of the barrier film 104.

The barrier film as described herein refers to a film laminated over alight emitting element to protect the light emitting element fromexternal contaminants or moisture. The barrier film is separate anddistinct from the encapsulation of the light emitting element.

The protective coating layer 132 should have a sufficient flexibility tobe used in the bend part of the flexible display 100. Further, theprotective coating layer 132 may be formed of a material which is curedat a low energy within a limited time so that components disposedtherebelow are not damaged during the curing process. For example, theprotective coating layer 132 may be formed of a photo (for example, UVray or visible ray) curable acryl resin. In order to suppress permeationof the moisture through the protective coating layer 132, one or moremoisture absorbing materials (getter) may be mixed to the protectivecoating layer 132.

Various resin application methods to apply the protective coating layer132 on a determined surface, such as a slit coating method or jettingmethod, may be used. As another example, the protective coating layer132 may be applied using a spraying valve. An application rate from thespraying valve may be adjusted during the coating process to preciselycontrol the thickness and diffusion of the protective coating layer 132.Further, the number of spraying valves which apply the protectivecoating layer 132 is not specifically limited. The number of sprayingvalves may vary so as to adjust a diffusion amount and an applicationtime before the protective coating layer 132 is cured.

FIG. 13A illustrates a configuration of the protective coating layer132. As mentioned above, the protective coating layer 132 may be coatedin the region between the barrier film 104 and the printed circuit board134 attached in the inactive area. However, depending on an adhesioncharacteristic and an intensity of stress of the protective coatinglayer 132, the protective coating layer 132 may be separated from thebarrier film 104 and/or the printed circuit board 134. An open spacebetween the protective coating layer 132 and the barrier film 104 or theprinted circuit board 134 may serve as a defective region into whichmoisture may be permeated.

Therefore, in some embodiments, the protective coating layer 132 may bedisposed to partially overflow above the barrier film 104, asillustrated in FIGS. 13A to 13C. That is, a part of the upper surface ofthe edge of the barrier film 104 may be covered with the protectivecoating layer 132. A region which is in contact with the surface of thebarrier film 104 suppresses the separation of the protective coatinglayer 132 from the barrier film 104 due to the bend stress. Improvedsealing provided by the protective coating layer 132 at the edge of thebarrier film 104 may reduce corrosion of the conductive lines in thebend portion. Similarly, the protective coating layer 132 may be appliedabove at least a part of the printed circuit board 134 to improve thesealing of the edge of the printed circuit board 134.

Referring to FIGS. 13B and 13C, a width of a region on the barrier film104 covered with the protective coating layer 132 is denoted by “W1” anda width of a region on the printed circuit board 134 covered with theprotective coating layer 132 is denoted by “W2”. A size (area) of theprotective coating layer 132 which covers the barrier film 104 and theprinted circuit board 134 is not specifically limited and may varydepending on an adhesiveness of the protective coating layer 132.

As illustrated in FIG. 13B, the flexible display 100 may include a partof the protective coating layer 132 on the barrier film 104 which isspaced apart from the edge of the polarization layer 110. However, insome embodiments, as illustrated in FIG. 13C, the flexible display 100may include a part of the protective coating layer 132 on the barrierfilm 104 which is in contact with the polarization layer 110.

A diffusing force of the applied protective coating layer 132 isdetermined not only by the viscosity but also by a surface energy of alocation where the protective coating layer 132 is applied. Theprotective coating layer 132 which overflows above the barrier film 104may reach the polarization layer 110. The protective coating layer 132which is in contact with a side wall of the polarization layer 110 mayhelp to fix the polarization layer 110 in place. However, the protectivecoating layer 132 which reaches the side wall of the polarization layer110 may be disposed above the side wall of the polarization layer 110.The side wall wetting of the protective coating layer 132 may generateuneven edges on the surface of the polarization layer 110, which maycause various problems when another layer is disposed thereon.Therefore, an amount of the protective coating layer 132 which isapplied on a specific surface may be adjusted so as to control thewidth. Furthermore, the protective coating layer 132 may be applied suchthat only some of selected regions of the polarization layer 110 are incontact with the protective coating layer 132.

In one configuration example, the protective coating layer 132 may be incontact with the polarization layer 110 at two opposing corners(“POL_CT” in FIG. 13A), but the protective coating layer 132 does notreach the edge of the polarization layer 110 between two corners. Theprotective coating layer 132 between two opposing corners POL_CT coversonly a part of the barrier film 104. After the bending process, a partof the flexible display 100 in which the protective coating layer 132 isspaced apart from the polarization layer 110 may be configured asillustrated in FIG. 14A. In a region configured such that the protectivecoating layer 132 is in contact with the polarization layer 110, theflexible display 100 may be configured as illustrated in FIG. 14B.

FIGS. 15A and 15B are views illustrating a protective coating layer usedfor a flexible display according to another embodiment of the presentdisclosure.

The protective coating layer 132 illustrated in FIGS. 13 and 14 has astructure which a specific resin is applied on the bend portion of thebase layer 106. In the above structure, when the protective coatinglayer is in contact with the side wall of the polarization layer 110, awetting phenomenon due to a surface tension may occur so that theprotective coating layer is applied so as to slightly cover the barrierfilm 104. By doing this, the above-described structure is applied to asmall size flexible display (for example, a smart watch) which has asmall horizontal width and has a barrier film and easily secures thecoating surface uniformity.

In contrast, the flexible display illustrated in FIG. 15A may beimplemented by a structure in which the polarization layer 110 isstacked on the base layer 106 (above the organic light emitting element)without a barrier film. This structure follows a development trend ofomitting the barrier film in order to apply a new encapsulationstructure and/or reduce a thickness. An adhesive layer 113 is located onthe polarization layer 110, and a cover layer may be disposed thereon.

The structure as illustrated in FIG. 15A may be applied to a largerflexible display (for example, a smart phone). However, as describedabove, when the protective coating layer 132 is applied in the structurein which the barrier film is omitted as in the related art, wetting dueto the surface tension may be caused on the side wall of thepolarization layer 110 and/or the adhesive layer 113. Accordingly, asillustrated in FIG. 15B, thickness non-uniformity of the protectivecoating layer 132 may be generated in several spots A, B, and C.Moreover, when the thickness of the protective coating layer 132 is notuniform, the neutral plane varies, which may become a potential factorcausing cracks.

FIGS. 16A to 16D are views illustrating a protective film used for aflexible display according to an embodiment of the present disclosure.

The flexible display may include a base layer 106, a polarization layer110, an adhesive layer 113, a protective film 140, and a printed circuitboard 134. In some embodiment, the flexible display may further includea supporting layer 108 and a supporting member (for example, a mandrel).When the base layer 106 is formed of plastic, the base layer may also bereferred to as a plastic film or a plastic substrate. For example, thebase layer 106 may be a film type layer including one selected from agroup consisting of a polyimide based polymer, a polyester basedpolymer, a silicon based polymer, an acrylic polymer, a polyolefin basedpolymer, and a copolymer thereof. Among these materials, polyimide maybe applied to a high temperature process and may be coated, thuspolyimide is widely used for a plastic substrate.

The base layer 106 of the flexible display may include a first portion101 and a second portion 102 as illustrated in FIGS. 3A and 4. In FIGS.3A and 4, it is illustrated that the second portion 102 extends to theoutside of the first portion 101, but the spirit of the presentdisclosure is not limited thereto. The first portion 101 is asubstantially flat portion on which the organic light emitting element,the polarization layer 110, and the adhesive layer 113 are disposed. Inthis case, the organic light emitting element, the polarization layer110, and the adhesive layer 113 are disposed on a first surface (a topsurface) of the first portion 101. The adhesive layer 113 may be a filmshaped transparent adhesive agent such as an optical clear adhesive(OCA). In the organic light emitting element, the first electrode, theorganic light emitting layer, and the second electrode are sequentiallydisposed. That is, the organic light emitting element may be configuredby a first electrode which is electrically connected to the driving thinfilm transistor (driving TFT), an organic light emitting layer which isdisposed on the first electrode, and a second electrode which isdisposed on the organic light emitting layer. The polarization layer maybe disposed on the organic light emitting element without having thebarrier film.

The second portion 102 is a portion which is bent toward a secondsurface (a bottom surface, which is opposite to the first surface) ofthe first portion 101. In this case, the second portion 102 may beprovided to begin (extend) from the outside of the first portion 101.The second portion 102 may be configured by a bend allowance sectionwhich is bent at a predetermined curvature and a flat section which isnot bent and is disposed below the first portion.

The protective film 140 covers at least a part of the second portion 102to suppress permeation of the moisture. Even though the protective film140 is applied to a large size display device (for example, a diagonallength of the first portion is four inches or longer), an improvedthickness uniformity thereof is achieved. For example, the protectivefilm 140 is not formed by applying a flexible resin in the bendallowance section, but formed by attaching a pre-fabricated film ontothe bend portion. Furthermore, a part of the second portion 102 on whichthe protective film 140 is not attached is covered with the resin 138,so that the permeation of the moisture is reduced.

The pre-fabrication of the protective film 140 is performed in anenvironment that is finely controlled and may go through additionalprocesses to improve the thickness uniformity of the film compared toforming a micro-coating layer on the bend allowance section by coatingthe bend allowance section with a resin and solidifying the resin.

The protective film 140 may be formed of a multi-layered film asillustrated in FIGS. 16C and 16D. In this case, the protective film 140may include an adhesive layer 143 which is in contact with the baselayer, a protective substrate 142 on the adhesive layer 143, and acushion layer 141 on the protective substrate. The adhesive layer 143may be formed of a material such as a pressure sensitive adhesive (PSA).The protective substrate 142 may be made of an elastomer based and/orpolyimide based material. The cushion layer 141 is provided to absorb animpact applied during an assembling/delivering process and may be formedof a material such as a foam rubber. The protective film 140 may includemoisture absorbing materials (e.g., a getter material).

The bend portion is subjected to a compressive stress and/or tensilestress above and/or below a neutral axis. Further, when thethickness/physical properties of the adhesive layer/protectivesubstrate/cushion layer vary, the position of the neutral axis may bechanged. Therefore, the protective film 140 may have uniform thicknessand density determined in consideration of the tensile stress which isapplied to the second portion (bend portion). For example, thethickness/density of the protective film 140 may be determined such thatthe conductive line and/or the inorganic layer on the second portion islocated above the neutral axis or below the neutral axis (a compressiveside). FIG. 16C is a view enlarging portion D of FIG. 16B and is anexample designed such that the adhesive layer 143 of the protective film140 is disposed on the neutral axis.

The resin 138 may be filled between the protective film 140 and thepolarization layer 110. In this case, the thickness of the resin 138 maybe equal to the thickness of the polarization layer 110 or slightlylarger than the thickness of the polarization layer 110.

As illustrated in FIGS. 16A and 16B, the printed circuit substrate 134may be connected to the second portion 102 at the outside of theprotective film 140. In the printed circuit board 134, componentsrelated to the operation of the organic light emitting element, such asa driver IC chip may be mounted. The printed circuit board is referredto as a chip on film (COF).

The resin 138 may be filled between the protective film 140 and theprinted circuit board 134. In this case, the resin 138 may be providedto cover one side (edge) of the protective film 140 and one side (edge)of the printed circuit board 134. The conductive line which connects thedriver IC chip and the organic light emitting element is disposed in thesecond portion (bend portion) and the protective film 140 covers theconductive line.

In some embodiments, differently from FIGS. 16A and 16B, the driver ICchip may be disposed on the base layer 106 at the outside of theprotective film in the second portion. That is, the driver IC chip maybe formed directly on the base layer 106.

Although the embodiments of the present disclosure have been describedin detail with reference to the accompanying drawings, the presentdisclosure is not limited thereto and may be embodied in many differentforms without departing from the technical concept of the presentdisclosure. Therefore, the embodiments of the present disclosure areprovided for illustrative purposes only but not intended to limit thetechnical spirit of the present disclosure. The scope of the technicalspirit of the present disclosure is not limited thereto. Therefore, itshould be understood that the above-described embodiments areillustrative in all aspects and do not limit the present disclosure. Theprotective scope of the present disclosure should be construed based onthe following claims, and all the technical concepts in the equivalentscope thereof should be construed as falling within the scope of thepresent disclosure.

What is claimed is:
 1. A flexible display, comprising: a base layerincluding a first portion having a first surface on which an organiclight emitting element is disposed and a second portion extending fromthe outside of the first portion and bent toward a second surfaceopposite to the first surface; a protective film covering at least apart of the second portion to suppress permeation of moisture; apolarization layer disposed on the organic light emitting element of thefirst portion without a barrier film between the polarization layer andthe base layer; and a resin filled between the polarization layer andthe protective film.
 2. The flexible display according to claim 1,wherein the protective film is a multi-layered film.
 3. The flexibledisplay according to claim 2, wherein the protective film includes anadhesive layer in contact with the base layer, a protective substrate onthe adhesive layer, and a cushion layer on the protective substrate. 4.The flexible display according to claim 2, wherein the cushion layer ismade of a rubber.
 5. The flexible display according to claim 3, whereinthe protective film has a uniform thickness and density determined basedon tensile stress applied to the second portion.
 6. The flexible displayaccording to claim 1, further comprising a printed circuit boardconnected to the outside of the protective film in the second portionand a driver integrated circuit (IC) chip mounted on the printed circuitboard.
 7. The flexible display according to claim 6, further comprising:a resin filled between the protective film and the printed circuitboard.
 8. The flexible display according to claim 6, further comprisinga conductive line disposed on the second portion and connecting thedriver IC chip and the organic light emitting element, wherein theprotective film covers the conductive line.
 9. The flexible displayaccording to claim 6, wherein the resin comprises a first part and asecond part, the first part covering a side of the polarization layerand a first side of the protective film, and the second part covering asecond side of the protective film and one side of the printed circuitboard.
 10. The flexible display according to claim 1, further comprisesa driver integrated circuit (IC) chip disposed at the outside of theprotective film in the second portion.
 11. The flexible displayaccording to claim 10, wherein the protective film includes a moistureabsorbing material.
 12. The flexible display according to claim 1,wherein the protective film is pre-fabricated and attached to at least apart of the second portion of the base layer.
 13. A flexible display,comprising: a base layer including a flat portion and a curved portionconnected to the flat portion; an organic light emitting elementdisposed on the flat portion of the base layer; a polarization layer onthe organic light emitting portion; a protective film on the curvedportion of the base layer; and a resin between the polarization layerand the protective film, the resin in contact with at least a sidesurface of the polarization layer and a first side surface of theprotective film.
 14. The flexible display of claim 13, wherein theprotective film includes: an adhesive layer on the curved portion of thebase layer for attaching the protective film to the curved portion ofthe base layer; a protective substrate on the adhesive layer; and acushion layer on the protective substrate for absorbing impact on theprotecting coating layer.
 15. The flexible display of claim 13, whereinthe protective film has a uniform thickness or a uniform density. 16.The flexible display of claim 13, further comprising: a printed circuitboard coupled to another flat portion of the base layer, the other flatportion connected to the curve portion at an opposite side of the flatportion; and a second resin between the protective film and the printedcircuit board, the second resin in contact with a side surface of theprinted circuit board and a second side surface of the protective filmat an opposite side of the first side surface.
 17. The flexible displayof claim 16, further comprising: one or more conductive lines disposedon the curved portion of the base layer, at least a portion of the oneor more conductive lines covered by the protective film, wherein the oneor more conductive lines couple the printed circuit board to the organiclight emitting element.
 18. The flexible display of claim 13, whereinthe protective film includes a moisture absorbing material.
 19. Theflexible display of claim 13, wherein a compressive stress is applied tothe base layer and a tensile stress is applied to the protective film.20. The flexible display of claim 13, wherein a thickness of the resinis equal to, or greater than a thickness of the polarization layer. 21.The flexible display device of claim 13, wherein a curvature radius ofthe substantially flat portion of the base layer is larger than acurvature radius of the curved portion of the base layer.